Biocorrosion was suspected in the corrosion failure of a cooling system of a stainless piping welded joint, carrying marine water. Marine water, which is used for cooling water in a plant was transferred to the laboratory and used for experiments. In the first experiment, weld metal samples were exposed to the test solution for 56 days (marine water and sterilized marine water (control)). The surface condition of experimental coupons was observed using a Scanning Electron Microscope (SEM). In another experiment, the free corrosion potential of these materials was monitored for 56 days. Pitting corrosion was found in the coupons exposed to marine water. Free corrosion potential ennoblement was found to be significant compared to the controls. It was suspected that this corrosion case was biocorrosion. In the second experiment, coupons were exposed to diluted nutrient medium containing single cultures of microbes isolated from the biocorrosion causing marine water sample used for the first experiment. After the exposure test, surface condition of the experimental coupon was observed using SEM. Pitting corrosion sites was found in coupons exposed to some of the isolates. The results indicate that they contribute to the corrosive effect of the SUS316L welds.
